1. Field of the Invention
The present invention relates to a liquid emission recording apparatus, and more particularly to a liquid emission recording apparatus (hereinafter called "ink jet recording apparatus") of so-called serial type in which the recording is conducted by moving a recording head, provided with discharge openings for recording liquid (hereinafter called "ink"), in a predetermined direction with respect to a recording medium.
More specifically the present invention relates to an ink jet recording apparatus equipped with capping means for preventing emission failure due to blockage of discharge openings caused by highly viscous ink, solidified ink, dust, bubbles etc., or with an emission recovery or restore device for resolving emission failure of the ink utilizing said capping means.
Also the present invention relates to an ink jet recording apparatus in which the driving source for feeding the recording sheet is utilized also for other purposes, such as for a recovery system for protecting the face of discharge openings of the recording head and for eliminating the ink solidified or viscosified in the discharge openings.
2. Related Background Art
In the conventional ink jet recording apparatus of this kind, the recording elements of the recording head mounted for example on a carriage may cause blocking or clogging in the discharge openings for example resulting from an increase in the ink viscosity due to the evaporation of solvent in the ink, thus resulting in defective recording or ink emission failure. For this reason, when the recording operation is not being conducted, the face of the recording head bearing the discharge openings is covered with a cap.
Among such apparatus, there is known an apparatus equipped with a mechanism for effecting the capping operation in relation to the movement of a carriage, supporting the recording head, to a predetermined position (for example home position). Such structure is advantageous in simplifying the construction of the apparatus, and reducing the manufacturing and running cost of the apparatus, since the movement of the capping member does not require a particular driving source such as a motor.
In such structure, the capping operation is forcedly conducted after the lapse of a predetermined time or upon detection that the recording head is out of a certain position, in order to prevent the drying of the recording elements in the stand-by state after recording. In such case the carriage motor for driving the carriage is driven with a low current.
However, thereafter a disabled recording start may occur due to the disrupted balance of surface tension of the ink in the vicinity of the discharge openings, caused by temperature increase in the recording elements in the capped state or by increase in the saturated vapor pressure of the ink in the capped space. For this reason, the space enclosed by the cap is made to communicate with the exterior after the lapse of a predetermined time. Thereafter, the holding of the phases of the carriage motor is interrupted, in order to prevent temperature increase thereof.
There is also known a structure in which, if an instruction for the recovery operation is entered from a data input unit within a predetermined time after the capping operation is started, a sheet feeding motor which is also used for recovery operation is reversed to suck the ink from the vicinity of the discharge openings thereby effecting the recovery operation.
However, in such conventional structure in which the exterior communicating operation and the recovery operation are started independently, the carriage motor may not be in the hold state if the communicating operation is conducted prior to the instruction for recovery operation from the data input unit. For this reason, the carriage may be out of the home position where recovery operation is conducted in proper manner, so that the recovery operation may not be achieved in proper manner after the communicating operation.
Also in the above-explained structures, the capping mechanism functions in response to the engagement of a part of the carriage and a part of the capping member, and a biasing force is applied in order to maintain the carriage in the capped state. It may however be difficult to securely maintain the capped state for example due to eventual play in the component parts.
As explained above, the ink jet recording apparatus utilizes ink as a medium, and effects recording by discharging ink from discharge openings of a recording head onto a recording medium such as paper or overhead projector sheet. However, if non-recording state continues, evaporation of the solvent component of the ink from the discharge openings induces an increase in the ink viscosity or eventual solidification of the ink, so that the ink emission may become difficult or impossible when the recording signals are entered.
A recovery system is therefore provided in order to eliminate the highly viscous or solidified ink in the discharge openings and to prevent the above-mentioned drawbacks. Said recovery can be achieved, for example, by fitting a capping member on the head face having the discharge openings and generating a negative pressure by a pump connected to said capping member. This action forcibly sucking the ink from said discharge openings and thus eliminating the solidified layer of ink.
This method is effective when the solidified layer of ink is thin. However, if the non-recording state continues for a considerably long time, said solidified layer becomes thick and exceeds a limit removable with the negative pressure of the pump, so that the recovery may become impossible. For this reason there is proposed a method called "major recovery". On the other hand, the above-mentioned method is called "minor recovery". The major recovery is conducted by filling a closed space formed by the head face having the discharge openings and the cap member with ink, then leaving the entire system for a suitable period for softening the solidified layer of the ink, and effecting suction operation in this state thereby removing the solidified layer of the ink.
In this major recovery operation, said closed space is filled with fresh ink directly supplied from an ink supply source such as an ink cartridge. For this purpose there are provided a tube for ink supply from the ink cartridge to the capping member, and switch means such as a valve for enabling ink supply through said tube only in the major recovery operation. The minor and major recoveries are switched by the open/closing operation of said valve. Said open/closing operation of the valve has been conducted by a solenoid valve, a motor-driven cam, or by the movement of a carriage supporting the recording head particularly in case of a serial ink jet recording apparatus.
However, the use of a solenoid valve for the above-mentioned switching operation results in an increased cost because the solenoid valve is expensive. Also the use of a motor-driven cam not only results in an increased cost due to the presence of a motor but also may reduce the throughput of the recording operation, since the operating speed is lowered.
On the other hand, the valve operation by the carriage movement is relatively effective since the operating speed is high and there are required few components leading to cost increase. However, there is required a transmission mechanism, such as a lever for valve operation, so that it is difficult to reduces the size of the recovery unit, or the entire ink jet recording apparatus.
Also for removing the highly viscous or solidified ink from the discharge openings of the ink jet recording head, there is known a method of covering the head face having discharge openings with an elastic cap, and sucking ink from the discharge openings by a negative pressure generated by a pump communicating with said cap, thereby eliminating the defective emission. Said pump may be driven by an exclusive motor for the recovery system, but is usually driven by a motor for feeding the recording sheet, for the purpose of both size and cost reduction of the apparatus.
For this purpose, at an end of a roller for feeding the recording sheet, there is provided a spring clutch for transmitting the driving force in the reverse rotation opposite to the rotation for sheet feeding, so that the motor effects sheet feeding in the forward rotation and drives the pump of the recovery system in the reverse rotation.
Said sheet-feeding motor also serves to drive a separating roller for sheet feeding, and is provided with a one-directional spring clutch in the transmission to said separating roller. The transmission of the driving force is turned off when a finger member engages with a part of said spring clutch, and is turned on when said finger member disengages. The sheet feeding operation is started by disengaging said finger member with a plunger or a carriage supporting the recording head, and is terminated when the spring clutch engages with said finger member again after the rotation of the separating roller.
In such conventional structure, when the sheet-feeding roller is reversed for activating the pump, the sheet-feeding spring clutch is supposed to slip and remain in the engaging position with the finger member. In practice, however, said spring clutch may also be reversed together with the roller and become unable to retain the initial state of sheet feeding engaged with the finger member, for example due to an increased slipping torque resulting from fluctuation in the manufacture of the spring clutch or a fluctuation in the load torque of the entire sheet feeding unit.
Consequently, when the finger member is disengaged by the plunger or the carriage at the sheet feeding operation, the sheet feeding operation is terminated before the separating roller reaches the normal rotational position. This may result in defective sheet feeding, or, in worst case, a situation where the sheet feeding is impossible.
As already explained above, in an ink jet printer for effecting the recording operation by flying ink droplets from discharge openings of the recording head according to recording data, there is provided an emission recovery mechanism for supplying ink to the discharge openings under pressure or sucking the ink from said discharge openings, in order to prevent ink solidification or dust deposition in the vicinity of the discharge openings.
FIG. 1 is a schematic perspective view of an ink jet printer provided with a conventional recovery or restore unit. In FIG. 1, a recording head 101 provided with plural ink discharge openings is mounted on a carriage 102, which is guided by a pair of guide rails 103 fixed on side plates (not shown) and is moved in a direction A by a wire 104 driven by a drive source (not shown). Rollers 106, 108 serve to transport a recording medium 107. An emission recovery unit 105 is equipped with a cap 116 movable in a direction B (B' or B") by means of a drive source (not shown), and effects ink suction in a state in which said cap 116 is fitted on the head 101.
In the emission recovery operation, the carriage 102 starts to move from a position in the recording area, for effecting the recording operation on the recording medium 107, to the illustrated position. In this state the cap 116 is retracted in a direction B' and housed in the emission recovery unit 105. After the carriage 102 is stopped at the illustrated position, the cap 116 is moved in a direction B" for example by a motor and contacts front end portion 101A of the recording head 101. The cap 116 is composed of a flexible material, and seals the ink discharge openings at the front end portion 101A of the recording head 101 from the exterior. When the emission recovery unit 105 generates a negative pressure in this state, the ink is sucked out from the recording head 101, thereby eliminating the cause of emission failure such as clogging of the discharge openings.
In such conventional structure, however, the pressure of the cap 116 is totally received by the front end portion 101A of the recording head, so that the recording head 101 or the cap 116 may be deformed by the repeated capping operation, thus becoming unable to maintain the sealed state and deteriorating the sucking effect. Also it may become difficult to maintain an appropriate distance (0.3-20 mm) between openings and the recording surface at the recording operation, if a strong pressure is applied to the recording head.
Consequently, in order to achieve the complete sealing by withstanding the pressure at the capping operation, it is necessary to increase the rigidity of the carriage 102 and the guide rail 103, and the supporting rigidity between the recording head 101 and the carriage 102. These components have to be made larger particularly in a color recording apparatus employing plural recording heads 101 according to the number of colors, and an increase in the dimension of the apparatus and an increase in the cost thereof are unavoidable.